The immune response to insulin provides a model system that is unique among well-studied antigens. The long-term objective of this study is to exploit novel aspects of this immune response to gain a deeper understanding of the cellular and molecular mechanisms responsible for regulating the magnitude and specificity of immune responses to insulin and other antigens. Major T cell determinants in insulin are generated during antigen processing by reduction of disulfide bonds with no requirement for proteolytic cleavage. The first aim is to characterize immunodominant T cell determinants in insulin recognized by mouse and human T cells using functional assays and biochemical techniques. Emphasis is placed on defining the role of cysteine thiol groups in antigen processing and T cell recognition. The second aim is focused on analysis of the effect of MHC polymorphism on the magnitude and specificity of the immune response to insulin. The third aim is to characterize a second peptide-binding site in class II MHC that may be used to present insulin B chain peptides and other antigens to a subset of T cells. The functional significance of alternative pathways for antigen presentation and the potential relationship with superantigen presentation will be explored. It is expected that the proposed study will broaden our general understanding of how antigen processing events, self tolerance, and MHC polymorphism affect the specificity and magnitude of immune responses.